A kind of preparation method of mcm-48 mesoporous molecular sieve

Abstract

The invention discloses a preparation method of an MCM-48 mesoporous molecular sieve. In the preparation method, cetyl trimethyl p-toluenesulfonate salt (CTATos) is used as a cationic surfactant, and the molar ratio of raw materials is as follows: SiO2/CTATos/NaOH/H2O = 1:(0.05-0.07):(0.5-0.67):(80-200). The preparation method comprises the specific steps: firstly dissolving silicon sol in an aqueous solution containing sodium hydroxide and stirring at the constant temperature of 60 DEG C for 1 hour; then adding dropwise the solution to an aqueous solution containing the surfactant and then further stirring at the constant temperature of 60 DEG C for 2 hours; after cooling to room temperature, transferring to a sealed reactor, and crystallizing at the temperature of 80-130 DEG C for 15 to28 hours; and finally filtering the crystallized product, washing, drying and then baking at the temperature of 550-900 DEG C for 3-6 hours to obtain the MCM-48 molecular sieve. Compared with the prior art, the preparation method disclosed by the invention has the most significant advantage that: CTATos is used as the cationic surfactant, thus greatly reducing the use amount of the surfactant in a synthesis system; in addition, the synthesis method provided by the invention has short synthesis period, low cost and good reproducibility; the synthesized product has extremely high hydrothermal stability; and the synthesis method is environmentally friendly.

Description

technical field [0001] The invention relates to a preparation method of a molecular sieve, in particular to a preparation method of a silicon-based mesoporous molecular sieve MCM-48 with high thermal stability. Background technique [0002] M41S series mesoporous molecular sieve materials, including MCM-41 with one-dimensional hexagonal channel structure, MCM-48 with three-dimensional cubic topology and MCM-50 with layered structure, were first successfully developed by Mobil in 1992. Due to the regular pore structure and large specific surface area (~1000m 2 / g), pore volume (1.0ml / g) and adjustable pore size (2.0-50nm) have aroused extensive research interest in the fields of catalysis, adsorption and separation. Since MCM-48 has a three-dimensional continuous pore structure, it has greater advantages and application prospects in molecular diffusion compared with the one-dimensional pore MCM-41 mesoporous material. However, due to the relatively narrow synthesis phase re...

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Problems solved by technology

However, due to the relatively narrow synthesis phase region of MCM-48, the synthesis conditions are extremely harsh, the reproducibility is poor, and the synthesis cost is high, which greatly limits the application range of MCM-48.

The current main synthetic strategies for the synthesis of MCM-48 include: using a single cationic surfactant (Chem. Mater., 1994, 6, 2317.), such as cetyltrimethylammonium bromide (CTABr), surfactant / The molar ratio of silicon is between 0.65-1.5, the synthesis cost is extremely high, and a large amount of foam is generated in the post-treatment process, and the separation is extremely complicated; the synthesis strategy of mixed template can greatly reduce the amount of cationic surfactant, but the two The molar ratio is difficult to control, so that it is difficult to synthesize high-quality MCM-48 mesoporous molecular sieves (Chinese patent, CN1188689A;); synthesis of new surfactants, such as Gemimi surfactants, can greatly reduce the amount of surfactants, However, the synthesis procedure of the surfactant is complex and the yield is low, which is not conducive to the synthesis of large-scale mesoporous molecular sieves (Chem. Mater., 1996, 8, 1147.); recently Chinese patents reported the use of F - MCM-48 mesoporous material (CN1775673A) can be effectively synthesized as an organic additive, but the presence of a large amount of fluoride ions is not friendly to the environment

In addition, cetyltrimethylammonium bromide (CTABr) as a template molecule to synthesize MCM-48 mesoporous materials usually has the disadvantage of poor hydrothermal stability, 550 o C roasted for 6 hours or refluxed in boiling water for 12 hours, most of the structure has collapsed, further hindering its industrial application

It can be seen from the above reports that the existing synthetic methods have the disadvantages of extremely harsh conditions, high cost, large pollution, and poor hydrothermal stability of the final product.

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